Thermostatic device



Dec. 11, 1951 H- ALLOY 0 AGE HARDENED NITR/DED sue/-74 c5 N/TRIDEDINTER/012 mi N W. A. MUD GE THERMOSTATIC DEVICE Filed April 10, 1946 FIG.I.-

am/2W FIG. 2.

L-2 ALLOY C AGE-HARDENED N/TR/DED sumac: N/TR/DED INTER/0R INVENTOR.WILLIAM ALVIN MUDGE AM ATTORNEX Patented Dec. 11,1951

THERMOSTATIC DEVICE William Alvin Mudge, New York, N.

Y., assignor to The International Nickel Company, Inc., New York, N. Y.,a corporation of Delaware Application April In 14 Claims.

The present invention relates to a composite metal temperatureresponsive device and more particularly to a thermostatic element to beused in a thermostat.

It is an object of the present invention to provide an improvedcomposite metal thermo static element.

It is another object of the invention to provide a bimetallicthermostatic element having improved strength.

It is still another object of the invention to provide a bimetallicthermostatic element having longer life.

It is a further object to provide a composite metal thermostatic elementhaving improved flexing properties 'by reason of better fatigueresistance.

It is also an object to provide an improved temperature responsivedevice, such as a thermostat, comprised of the composite metalthermostatic elements provided by the invention.

Other objects and advantages of the invention will be apparent to thoseskilled in the art from the following description taken in conjunctionwith the drawing which depicts two views in section of two bimetallicthermostatic elements each embodying the present invention.

Broadly stated, the present invention provides a thermostatic elementcomprising a plurality of metallic members of dissimilar coeflicients ofthermal expansion secured together in faceto-face relationship byrivets, spot welds, diffusion bonding, or other known manner, andadapted to act as a unitary element, at least one of said members beingmade of an agehardened alloy which is also nitrided throughout the crosssection of the member. By agehardened" is meant that the member is in ahardened condition resulting from a solution treatment at hightemperatures followed by a treatment at lower temperatures, the lattertreatment producing the hardening eifect. In the more commonage-hardenable alloys, agehardening is generally obtained by heating thealloy to a high temperature to place the precipitable phase in a solidsolution, followed by rapid cooling to preserve the solid solution andtreatment of the alloy at lower agin temperatures to precipitate theprecipitable phase in a critical finely dispersed state to causehardening. By "nitrided throughout the cross section" is meant that themember contains nitrogen diffused throughout the cross section of thememher. The invention is not limited to the agehardening and nitridingof only one member 1946, Serial No. 661,082 Canada March 15, 1946 Morethan one member can be age-hardened and nitrided. Thus, if thethermostatic element consists of two members, both can be agehardenedand nitrided throughout their cross sections. Likewise, if thethermostatic element consists of three or more members, more than onemember can be age-hardened and nitrided throughout the cross section.

Despite the fact that age-hardening markedly increases the hardness andlowers ductility accordingly, and that nitriding renders metals andalloys extremely hard, up to 1000 Vickers hardness number, with atendency to be brittle, I have discovered that when a member of athermostatic element is age-hardened and nitrided throughout the crosssection, better flexing properties are obtained. In addition, thethermostatic element made of at least one age-hardened and nitridedmember has a high equivalent yield strength. The equivalent yieldstrengt is considered by many in the art to be a very important propertywhich gives a good indication of the load-carrying capacity which willevaluate service life. The equivalent yield strength" is the stresswhich will give a composite metal thermostatic element a permanent setwhen the stress is removed. The degree of permanent set is considered bymany in the art to be the Proof Stress set, e. g. 0.01% permanentelongation. The. art has employed severe cold working or colddeformation to raise the equivalent yield strength. The age-hardened andnitrided members provided by the present invention have a higherequivalent yield strength than has been obtainable heretofore by coldworking. The age-hardened and nitrided members also have greaterstrength, better flexing properties and longer life, by reason ofimproved fatigue resistance. As a result of the improved properties, theinvention provides thinner thermostatic members, such as striplikemembers, than has been available heretofore.

In carrying the invention into practice, it is preferred that thesmaller cross sectional dimension of the age-hardened and nitridedmember not exceed about 0.03 inch. In order that this member benitridable, the sum total of the elements present which do not impartnitridability, e. g.-nickel, copper, chromium, molybdenum, tungsten,should not exceed approximately of the whole composition. On the otherhand, iron imparts nitridability to the member and is preferably presentin the comthe case of copper-base alloys, manganese,

' contain small amounts of ability. such as titanium, maganese, silicon,and aluminum act like iron in this respect. The greater the amount ofthose elements which are nitriding promoters, the more pronounced willbe the effects of nitriding, with respect to both nitrogen concentrationand rate of diffusion. The member to be age-hardened and nitrided ismade of an alloy containing approximately 2% to 80% of one or more ofthose metallic elements which do not impart nltridability, e. g. nickel,copper, chromium, molybdenum, tungsten; approximately 20% to 97% ofthese ele- 'ments which are nitriding promoters, e. g.

titanium, maganese, silicon, aluminum, and particularly iron; andcontaining at least one age-hardening element, e. g.-titanium, aluminum,silicon, beryllium, and magnesium, and i: an amount sufilcient to impartage-hardenability and nitridability to the alloy.

This invention particularly contemplates agehardened and nitridedmembers made of an ironnickel-titanium or an iron-nickel-chromiumtitanim alloy containing about 1% to 10% titaniup to about 25% chromium, about2% to 80% nickel, the balance being substantially iron in an amountconstituting at least 10% of the alloy, the sum of the nickel plus anychromium that may be present not exceeding approximately 80% of thewhole composition, and the sum of the iron plus nickel contents being atleast approximately 70% of the whole composition. An example ofdifferent types of alloys which also may be empolyed in accordance withthis invention as an age-hardened and nitrided member of thethermostatic element are the copper-nickel-manganese alloys, e. g.-60%copper, 20% nickel, and 20% manganese, such as are disclosed in theDean, United States patent, No. 2,234,552.

Illustrative examples of ranges of compositions which are preferablyemployed in accordance with the invention as the nitrided andage-hardened member of the thermostatic element are as follows:

A B O I) E Percent Ni... 40.5425 44. 5-40.15 51.0-53.0 2s.0-a0.041.0-43.0 Percent'li... 2.2-2.8 2.2- 2.8 2.2-2.8 2.2-2.8 2.2-2.8PereentAl... 0.4- 0.8 0.4-0.8 0.4-0.8 0.2-0.8 0.4-0.8 Per cent 8L.-.0.1- 0.8 0.1- 0.8 0. l- 0.8 0.1- 0.8 0.1- 0.8 Per cent Mn... 0.3- 0.00.3- 0.0 0. 3- 0.6 0.3- 0.0 0.3- 0.0 Per cent Cr... 8.0- 9.0 4.5- 6.5Per cent 0.... 0.1mm: 0.1max. lmax 0.1rnax. 0.1max. Per cent Fe. BalanceBalance Balance Balance Balance When it is stated herein that thebalance is iron or is substantially all iron, it is not intended toexclude small percentages of incidental elements and impurities such ascobalt, calcium, sulfur, phosphorus, etc. Thus, the compositions usuallysulfur and/or phosphorus. but it is preferred that the amounts of eachof these, when present, not exceed about 0.04%. Likewise, cobalt may bepresen Commercial nickel usually contains some cobalt in amounts up toabout 1% or more. The presence of cobalt in the amounts of the order ofis often beneficial in low-expansion iron-nickel alloys such as setforth hereinabove. Small amounts of calcium of the order of about 0.05%are often desirable to impart forgeability.

Alloy compositions A, B, and C in the axehardened and nitrided conditionare particularly suitable as the low-expansion member of thethermostatic element, for example,'members L4 and L-2 in the drawing.Alloy composition P in 1. constituent, e. g.,

the age-hardened and nitrided condition forms an excellent mghecxpansionmember, for example, member 11-! in the drawing. Alloy composition Ewhen age-hardened and nitrided throughout the cross section can be used/either as the low-expansion member or the high-expansion member. Thus,when used in combination with an age-hardened and nitrided member ofalloy composition A or B, any of the latter is the low-expansion member,and the member of composition E is the high-expansion member. when usedin combination with a member made of alloy composition C or D, thelatter is the high-expansion member, and the composition E member is thelow-expansion member. In all the foregoing examples, both thelow-expansion and the high-expansion member can be in the ace-hard-.ened and nitrided condition, or only one member need be in such acondition. ber could be in an age-hardened and nitrided condition whilethe other is ina non-nitrided but age-hardened condition. It ispreferred that both members be in an age-hardened and nitrided conditionprovided the expansion and other required properties will so permit.

when only one member is made of an agehardened and nitrided alloy, suchas compositions A to E, the other member can be a non-nitridablematerial, such as non-ferrous alloys. Illustrative examples of suitablenon-ferrous alloys include cupro-nickel, e. g., an alloy containingabout 30% to 45% nickel and about 55% to 70% copp r, and nickel-copperalloys sold under the trade-mark of "Monel" and containing abouttwo-thirds nickel and one-third 33% copper and about 63% to 73% nickel.Small amounts of age-hardening elements, e. g., aluminum and/ortitanium, may be present in the nickel-copper alloy, and such an alloyis sold under the trade-mark K Monel." The non-nitrided member can bemade of such an age-hardenable alloy composition. When cupro-nickel ornickelcopper alloys are employed as the non-nitrided member, that memberis the high-expansion member when the other member is made of anage-hardened and nitrided alloy of compositions A, B, C, or E, and isthe low-expansion member when the other member is made of anage-hardened nitrided alloy of composition D.

Illustrative examples of compositions suitable for use in strip-like orribbon-like form as the age-hardened 'and nitrided members in thethermostatic elements, and temperature responsive devices comprisedthereof, contemplated by the invention include the following:

Thus, one mem- I 4 111 IV v 42.0 45.0 02.0 20.0 42.0 24 a4 24 2.4 2.40.4 0.4 0.4 0.4 0.4 0.3 as 0.0 0.5 0.5 0.4 0.4 0.4 0.4 0.4 as 5.4

0.00 0.00 0.00 0.00 0.00 max. max. max. max. max. Per cent Fe B81. an.m0. an. an.

Compositions I to V are illustrative of alloys within the ranges ofcompositions A to E. respectively, and are all age-hardenable andnitridable. Age-hardening can be obtainodin all the compositions bytreatment for at least twenty minutes, e. g., one-half to one andone-half hours. within the solution temperature range of about 1700" F.to 1850 F., followed by cooling the alloy to preserve the solid solutionof the precipitable by a rapid cooling such as copper, e. g., about 26%to quenching, and thereafter treating the compositions within the agingtemperature range of about 1100 F. to 1350 F. to impart age-hardness, e.g., treating within said range for about three to forty-eight hours. Thecompositions can all be nitrided by treating them in an atmosphere ofdissociated ammonia, e. g., about 24% to 40% dissociation, at nitridingtemperatures between about 900 F. and 1200 F. for sufficient time tonitride the member throughout its cross section. Because the nitridingtemperatures overlap the aging temperatures, it is possible toage-harden and nitride the member simultaneously, e. g., at temperaturesof about 1100 F. to 1200 F. In other words, after treatment tosimultaneously in an age-hardened and nitrided condition throughout itscross section.

The age-hardened and nitrided member can advantageously be subjected toan additional shot-peening treatment to improve further the strength andperformance of the thermostatic element. The shot-peening treatment canbe accomplished by the usual methods, and its effect is superimposed onthose derived from the agehardening and nitriding treatment whereby newand improved characteristics are obtained in thermostatic elements.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such variations and modifications are considered to bewithin the purview and scope of the invention and the appended claims.

I claim:

1. As a new article of manufacture, a bimetallic thermostatic elementcomprising a low-expansion member made of an iron-nickel alloycontaining about 40.5% to 53% nickel, about 2.2% to 2.8% titanium, about0.4% to 0.8% aluminum, about 0.1% to 0.8% silicon, about 0.3% to 0.6%manganese,a small amount up to about 6.5 chromium, a small amount up toabout 0.1% carbon and the balance substantially iron, and a highexpansion member made of an iron-nickel alloy containing about 28% to30% nickel, about 2.2%

to 2.8% titanium, about 0.4% to 0.8% aluminum, about 0.1% to 0.8%silicon, about 0.3% to 0.6% manganese, about 8% to 9% chromium, up toabout 0.1% carbon and the balance substantially iron, said low-expansionmember and said highexpansion member both being in an age-hardened andnitrided condition throughout the cross sections of said members.

2. In a bimetallic thermostat the improvement which comprises making thelow-expansion member of said thermostat of an alloy containing about40.5% to 53% nickel, about 2.2% to 2.8% i a um. about 0.4% to 0.8%aluminum, about 0.1% to 0.8% silicon, about 0.3% to 0.6% manganese, asmall amount up to about 6.5% chromium, a small amount up to about 0.1%carbon and the balance substantially iron; said member having anage-hardened and nitrided structure throughout the cross sectionthereof.

3. In a bimetallic thermostat the improvement which comprises making thehigh-expansion member of said thermostat or an alloy containing about28% to 30% nickel, about 2.2% to 2.8% titanium, about 0.4% to 0.8%aluminum, about 0.1% to 0.8% silicon, about 0.3% to 0.6% manganese,about 8% to 9% chromium, a small amount up to about 0.1% carbon and thebalance substantially iron; said member having an agehardened andnitrided structure throughout the cross section thereof.

4. In a thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 28% to 53%nickel,about 2.2% to 2.8% titanium, about 0.4% to 0.8% aluminum. about0.1% to 0.8% silicon, about 0.3% to 0.6% manganese, a small amount up toabout 9% chromium, a small amount up to about 0.1% carbon, and thebalance substantially iron; said member having an agehardened andnitrided structure throughout the cross section thereof.

5. In a thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 2% to nickel, about 1%to 10% titanium, and the balance substantially iron, the sum of thetitanium plus iron contents being at least 20% of the alloy composition;said member having an age-hardened and nitrided structure throughout thecross section thereof.

6. In a thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 2% to 80% nickel,about 1% to 10% titanium, a small amount up to about 25% chromium, andthe balance substantially iron, the sum of the nickel plus chromiumcontents not exceeding approximately 80% of the alloy composition; saidmember having an age-hardened and nitrided structure throughout thecross section thereof.

7. In a thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 2% to 80% nickel,about 10% to 97% iron, about 1% to 10% titanium, the sum of the ironplus titanium contents being at least 20% of the alloy composition, thesum of the iron plus nickel contents being at least 70% of the alloycomposition; said mem-- ber having an age-hardened and nitridedstructure throughout the cross section thereof.

8. Ina thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 2% to 80% nickel,about 10% to 97% iron, a small amount up to about 25% chromium, about 1%to 10% titanium, the sum of the nickel plus chromium contents notexceeding approximately 80% of the alloy composition, the sum of theiron plus nickel contents being at least 70% of the alloy composition;said member having an age-hardened and nitrided structure throughout thecross section thereof.

9. In a thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 2% to 80% nickel,about 10% to 97% iron, and metal from the group consisting of aluminumand titanium in an amount within the range of about 1% to 10% suflicientto impart age-hardenability, the sum of the iron plus the metal fromsaid group being at least 20% of the alloy composition, the sum or theiron plus nickel contents beingat least 70%.of the alloy composition;said member having an age-hardened and nitrided structure throughout thecross section thereof.

10. In a thermostatic element having a plurality of members theimprovement which comprises making at least one member of saidthermostatic element of an alloy containing about 2% to 80% nickel,about to 97% iron, a small amount up to about 25% chromium, nd metalfrom the group consisting of aluminum and titanium in an amount withinthe range of about 1% to 10% suflicient to impart age-hardenability, thesum of the nickel plus chromium contents not exceeding 80% of the alloycomposition, the sum of the iron plus nickel contents being at least 70%of the alloy composition; said member having an age-hardened andnitrided structure throughout the cross section thereof.

11. In the method of producing a thermostatic element having a pluralityof strip members the improvement which comprises making at least onestrip member of said thermostatic element of an alloy containing about2% to 80% nickel, about 10% to 97% iron, and metal from the groupconsisting of aluminum and titanium in an amount within the range ofabout 1% to 10% sufllcient to impart age-hardenability, the sum of theiron plus the metal from said group being at least of the alloycomposition, the sum of the iron plus nickel contents being at least 70%of the alloy composition; said member having an age-hardened andnitrided structure throughout the cross section thereof; and joiningsaid strip member in face-to-face relationship with another strip memberof said thermostatic element.

12. In the method of producing a thermostatic element having a pluralityof strip members the improvement which comprises making at least onestrip member of said thermostatic element of an alloy contaning about 2%to 80% nickel, about 10% to 97% iron, a small amount up to aboutchromium, and metal from the group consisting of aluminum and titaniumin an amount within the range of about 1% to 10% sumcient to impartage-hardenability, the sum of the nickel plus chromium contents notexceeding about 80% or the alloy composition,

the sum of the iron plus nickel contents being at least 10% of the alloycomposition; said member having an agehardened and nitrided structurethroughout the cross section thereof: and joining this strip member inface-to-face relationship with another strip member of said thermostaticelement.

13. In a temperature-responsive device having a plurality of members theimprovement which comprises making at least one member of said device ofan alloy containing a small but effective amout up to about of metalfrom the group consisting of nickel, chromium and copper, about 1 toabout 10 2, of metal from the group consisting of titanium and aluminumand the balance consisting essentially of iron; said member having anage-hardened and nitrided structure throughout the cross sectionthereof.

14. In a temperature-responsive device having a plurality of members,the improvement which comprises making at least one member of saiddevice of an alloy containing a, small but effective amount up to about80% of metal from the group consisting of nickel, chromium and copper,and the balance essentially metal from the group consisting of titanium,aluminum, manganese, silicon and iron; said member having anage-hardened and nitrided structure throughout the cross sectionthereof.

WILLIAM ALVIN MUDGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

